Evidence exists to support a benefit of colorectal carcinoma screening. However, the currently available screening tests are compromised by limitations and there is less than optimal patient compliance to recommended screening algorithms. Currently, bowel preparation is the most important obstacle for compliance to colorectal screening guidelines. Techniques to evaluate the unprepared colon are being explored using conventional CTC, however several limitations may preclude its full clinical implementation. The broad long-term objective of this work is to develop a novel technique for imaging the colon without cathartic preparation at CT colonography with dual energy CT technology. Utilizing dual energy information regarding chemical material composition will allow easy discrimination between stool and polyps 1 cm or larger. Using advanced decomposition algorithms before reconstruction and intimate knowledge of the system performance we will assess this technique first in phantoms and then in patients as described in three related aims that will be conducted in series: 1) develop algorithms and calibrations for material decomposition using dual energy CT colonography data, 2) determine the feasibility to differentiate polyps from stool with or without the use of contrast agents, and 3) assess the feasibility and accuracy of the dual energy techniques in a pilot patient study. Investigative teams from Mayo Clinic-Rochester and GE Global Research will leverage their complementary skills in this collaborative project. The investigators have world-class expertise and resources in CT colonography, dual energy algorithms, and CT system calibrations. [unreadable] [unreadable]